1. Field of the Invention
This invention relates in general to hydrocarbon production, and more particularly, to identifying rock types and rock properties in order to improve or enhance drilling operations.
2. Description of the Related Art
Measuring rock properties during drilling in real time can provide the operator the ability to steer a drill bit in the direction of desired hydrocarbon concentrations. In current industrial practice and prior inventions, either resistivity or sonic logging while drilling (LWD) tools are employed to guide the drill bit during horizontal or lateral drilling. The center of these techniques is to calculate the locations of the boundary between the pay zone and the overlying rock (upper boundary), and the boundary between the pay zone and underlying rock at the sensors location. The drill bit is steered or maintained within the pay zone by keeping the drill string, at the sensors position, in the middle, or certain position between the upper and lower boundaries of the pay zone. The conventional borehole acoustic telemetry system, which transmits data at low rate (at about tens bit per second), is employed to transmit the measured data to surface.
Since the sensors are located 30-50 feet behind the drill bit, theses conventional LWD steering tools only provide data used in steering the drill bit 30-50 feet behind the drill bit. As the result, it is only after the 30-50 feet that the operator finds out if the selected drilling path is or is not the desired one. Therefore, these tools are not true real-time tools.
Some newer types of systems attempt to provide data at the drill bit, at real-time, while still utilizing conventional borehole telemetry systems (having a relatively slow bit rate). Such systems, for example, are described as including a downhole processor configured to provide downhole on-site processing of acoustic data to interpret the lithologic properties of the rock encountered by the drill bit through comparison of the acoustic energy generated by the drill bit during drilling with predetermined bit characteristics generated by rotating the drill bit in contact with a known rock type. The lithologic properties interpreted via the comparison are then transmitted to the surface via the conventional borehole telemetry system. Although providing data in a reduced form requiring only a bit rate speed, as such systems do not provide raw data real-time which can be used for further analysis, it is nearly impossible to construct additional interpretation models or modify any interpretation models installed on the downhole processor.
Some newer types of borehole data transmitting systems utilize a dedicated electronics unit and a segmented broadband cable protected by a reinforced steel cable positioned within the drill pipe to provide a much faster communication capability. Such systems have been employed into conventional LWD tools to enhance the resolution of the logged information. However the modified tools still measures rock properties at the similar location which is 30-50 feet behind the drill bit.
Accordingly, recognized by the inventor is the need for methods of identifying rock properties in real-time during drilling, and more particularly, methods that include employing/installing apparatus having acoustic sensors adjacent the drill bit positioned to detect drill sounds during drilling operations, a downhole computer/processor positioned to receive raw acoustic sensor data and to process the raw acoustic sensor data to determine acoustic characteristics, a telemetry system for pushing acoustic feature data to a surface computer and the computer/processor positioned to receive the acoustic characteristics data to derive the rock type and to evaluate the properties of the rocks in real-time. Recognized by the inventor is that the acoustic characteristics data would require a reduced bandwidth, sufficient enough to allow use of conventional bit-rate borehole telemetry systems, yet still hold important information previously considered available only through access to raw acoustic sensor data.